Cryogenic pump



April 23, 1968 R. c. WAGNER CRYOGEN IC PUMP 2 Sheets-Sheet 1 Filed Aug. 16, 1965 I N VE N TOR 6%97467/ zm M, MMSM April 23, 1968 R. c. WAGNER 3,379,132

CRYOGENIC PUMP Filed Aug. 16, 1965 2 Sheets-Sheet 2 IN VEN TOR /61 6 /5H 0% 7/ 5:7 A TTOR/VEYS Unit 1.

ABSTRACT F THE DISCLOSURE A cryogenic liquid circulation system is disclosed comprising a main housing mounting a dewar vessel therein for providing a thermally isolated sump for a reservoir of cryogenic liquid. Pumping mechanism supported from the main housing includes a depending shaft housing carrying a pump housing in submerged relation in the liquid and 9. depending shaft extending in clearance relation through the shaft housing and mounting an impeller for close clearance rotation in the pump housing. Adjustable mechanism on the main housing enables setting of the pump operating clearance. Gas lock is prevented by a vent passage leading from the impeller chamber through axial holes in a plastic shaft bearing, through clearance space between the shaft and shaft housing and through exposed holes in the shaft housing.

This invention relates to cryogenic liquid circulation apparatus and more particularly is concerned With an improved cryogenic liquid pumping arrangement suitable for low capacity requirements.

In current practice, cryogenic pumps are concerned exclusively with high capacity, high etliciency applications requiring extremely close tolerance designs and high cost parts and manufacturing techniques. Such devices or miniaturizations thereof are not suited for low capacity applications where pumping eificiency is of less importance and equipment cost is of greater importance.

The design problems inherent in any cryogenic liquid pump application are extremely diflicult of solution and such problems as suction, induced flashing and cavitation effects and thermal expansion and contraction effects long plagued the now rather well developed high capacity field. The solution in that field, however, are not of the same merit in the low capacity field because of the difference in emphasis on cost and efliciency.

In accordance with the present invention, a cryogenic liquid circulation apparatus is provided for the low capacity field. One such application is found in connection with flash freezing of food products by liquid nitrogen spray techniques. It is particularly effective to establish a spray flow rate substantially in excess of that required on the basis of the actual vaporization rate associated with freezing of the product. The augmented spray rate enables a more effective spray pattern and surface contact against the product to greatly improve the heat transfor rate. The excess liquid which does not flash to vapor is continuously collected and recirculated to sustain the desired spray discharge pattern without unacceptable losses in freezing efficiency. The present invention provides a liquid collection and pumping apparatus suited for this purpose.

In general, there is provided a thermally isolated sump having a centrifugal pump unit disposed therein normally to be submerged and subjected to a predetermined positive suction head for minimizing flashing and cavitation effects.

A main housing receives a dewar vessel to provide the sump and the main housing includes top support structure for suspending fixed and moving parts of the pump unit. The pump unit has a durable bearing arrangement d States Patent 0 Patented Apr. 23, 1968 including a special impeller end shaft bearing suited to the cryogenic environment and provided with vent passages for purging the pump chamber to relieve gas lock effects and an externally mounted drive end shaft bearing effectively protected from the cryogenic environment and adjustably mounted to effect close clearance setting of the pump parts for accommodating thermal expansion and contraction effects associated with initial fill and start up of the pump system.

A drive motor for the pump unit and a float type level sensing control for the motor maintain a predetermined liquid level in the sump and are provided in the main housing immediately alongside the dewar vessel to be thermally isolated while facilitating the requisite mechanical drive and float connections.

Other features and advantages of the invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which show structure embodying preferred features of the present invention and the principles thereof, and what is now considered to be the best mode in which to apply these principles.

In the accompanying drawings forming a part of the specification, and in which like numerals are employed to designate like parts throughout the same,

FIG. 1 is a vertical section illustrating one embodiment of a cryogenic liquid circulation apparatus of this invention;

FIG. 2 is a reduced top plan view of the apparatus illustrated in FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view taken as indicated on the line 3-3 of FIG. 2 and illustrating a float type liquid level control arrangement; and

FIG. 4 is an enlarged fragmentary vertical section better illustrating certain aspects of the pump mounting and drive mechanism.

Referring now to the drawings, one embodiment of cryogenic liquid circulation apparatus is designated genorally at 19 in FIG. 1 and includes a dewar vessel 11 providing a thermally isolated sump for maintaining a reservoir of cryogenic liquid 12 at a level such as is indicated at 12L. in the particular arrangement disclosed herein, liquid may enter the sump either through a fill line 13 (see FIG. 2) when the equipment is initially being charged or through a return drain line 14 which opens into the dewar vessel ii. A pump unit designated generally at 15 is shown submerged in the reservoir of liquid nitrogen 12, and has a pressure discharge line including a horizontal stub 15H, a right angle elbow 15B and a vertical riser 15R existing through the top of the dewar vessel 11.

In the flash freezing of food products by liquid nitrogen spray techniques, the riser 15R leads to an array of spray heads in a process chamber (not shown) and the return line 14 leads from a liquid collection trough (not shown) within such a process chamber. A typical value of mass flow in such a flash freezing application is 5,800 pounds per hour or 14 gallons per minute and the disclosed embodiment of the invention serves to provide capacity values of this general range.

In the disclosed embodiment, the pump unit 15 includes a pump housing 16 having a downwardly opening suction inlet 161 communicating with the reserve of liquid in the sump. A pump housing end plate 17 is fixed to the top of the pump housing 16 by one or more fasteners 17F and these elements collectively define a pump chamber C. The end plate 17 is fixedly carried at the lower end of a tubular shaft housing 18 which is suspended above the dewar vessel 11. A shaft 19 extends full length through the shaft housing 18 and terminates at a reduced lower end 19E which rotatably drives a centrifugal impeller that is to operate in close clearance relation within the pump chamber C.

The dewar vessel 11 is contained within a generally rectangular main housing structure, designated generally at 21, having side walls 218 and a top wall MT. The main housing 21 is of greater transverse dimension than the dewar vessel and provides a mounting chamber 22 alongside of the dewar vessel for receiving a drive motor 23 (FIG. 1) and a switch assembly 24 (FIG. 3) which is controlled by a float 25 located in the liquid and connected through a rigid three-sided linkage 26 which includes actuator rods 25A and 26B slidably movable through the top wall 21'1" to regulate the switch control in accordance with float position for maintaining the liquid level 12L.

The region of the top wall 21T that spans the dewar vessel 11 is reinforced by a stiffener rib 21R located within and adjacent the top edge of the dewar vessel 11. The upper shaft end i9U projects through a seal collar 27 mounted in a flanged disc 28 bolted against the underface of the top housing wall 21T. A drive belt 29 is provided for the pump shaft, it being trained about a drive pulley 30 at the upper end of a vertical motor shaft 235 and about a driven pulley 31 at the exposed upper end of the pump shaft 1%.

A thermal dissipation plate 32 is shown mounted on upstanding spacer sleeves 33 that are fastened to the top wall ZlT to locate the plate in thermally isolated relation above the main housing and to expose the plate surfaces to ambient air conditions. The dissipation plate is fitted with an upstanding fixed ring 34 having internal threading cooperable with a carrier disc 35 threading by engaging and rotatable with respect to the fixed ring 34 to undergo controlled movement in the direction of the pump shaft axis.

Rotation of the pump shaft is guided by upper and lower bearings 36 and 37, respectively, the upper bearing 36 being remote from the cryogenic environment but thermally exposed through direct contact with the pump shaft. The upper bearing 36, being mounted in heat transfer relation to the carrier disc 35, the ring 34 and the dissipation plate 32, may be of conventional ball bearing construction and includes inner and outer races retained by a snap ring 36R to support the pump shaft 19. The lower end bearing 37 is seated in a mounting pocket provided within the end plate 17 and is retained therein by a snap ring 37R. This lower bearing is of a lubric plastic material compatible with its cryogenic environment and in the disclosed embodiment has a nylon body impregnated with molybdenum dissulfide. The bearing 37 has a set of axially directed holes 37H in a regularly spaced annular array to establish venting communication between the pump chamber C and the lower end of the shaft housing 18. The vent passage is completed by side wall holes 18H provided in the shaft housing 18 at a location above the liquid level 12L so that liquid is not permitted to enter the shaft housing.

Assuming the pump is to be connected into a cryogenic liquid system, all of the elements are initially at ambient temperature and at this time, the clearance between the underface of the impeller 20 and the underlying horizontal wall of the pump housing 16 should be at a value which is to be maintained during steady state operation. Typically, the minimum dimension for this clearance to insure efficient pump operation is 0.030 inch. This clearance value is preset under ambient conditions by rotating the carrier 35 in a direction to bottom the impeller against the pump housing 16 and then reversely rotating the carrier 35 to lift the impeller a prescribed amount which accurately determines the desired clearance.

When a cryogenic liquid initially enters the sump and fills the same to the level indicated at 12L, the shaft housing 13 being directly exposed to the liquid shrinks an amount closely corresponding to the initial clearance so that the clearance reduces substantially to zero but is great enough to accommodate free impeller rotation during start up of the system. As the operation continues, the shaft 19, which is only indirectly exposed to the cryogenic liquid environment, ultimately contracts an equivalent amount until the initial clearance is reestablished.

At all times during pump operation, a positive suction head acts on the pump chamber C through the inlet opening 161. This head is regulated by control of the motor 23 through the means of the switch 24 and the float 25. This head is important in achieving an effective pumping of the cryogenic liquid and in minimizing gas lock due to flashing to vapor of such liquid when subjected to pump suction. Gas lock at the pump is an inherent problem with cryogenic liquids. Gas lock is relieved in the present arrangement by venting along a path beginning with the holes 37H provided in the lower bearing, leading upwardly through the shaft housing 18 and exiting through the vent holes 18H which communicate with the dewar vessel above the level of liquid maintained by the float 25.

The construction of the disclosed embodiment of the circulation appartus achieves good efiiciency by regulating pump clearances accurately. This is accomplished without expensive design and machine requirements by virtue of the easily adjusted carrier 35 which is located remote from the cryogenic environment, thus facilitating its own design and construction.

Thus, while preferred constructional features of the invention are embodied in the structure illustrated herein, it is to be understood that changes and variations may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

What is claimed is:

1. Cryogenic circulation apparatus comprising a main housing having a dewar vessel disposed therein and providing a thermally isolated sump for storing a reservoir of cryogenic liquid, said main housing also defining a chamber alongside the dewar vessel and exposed to normal ambient conditions, said main housing having a cryogenic liquid inlet opening into the sump, a cryogenic liquid discharge line emerging upwardly through the dewar and main housing, pumping mechanism carried by said main housing and including a shaft housing fixed to said main housing and extending vertically to terminate at a lower end submerged in the cryogenic liquid, said shaft housing having vent openings above the level of the liquid in the sump, a pump housing fixed on the lower end of said shaft housing and defining a pump chamber, said pump housing having an axial top pocket opening upwardly into the shaft housing, an axial bottom inlet opening into the sump and a peripheral discharge outlet communicating with said discharge line, a one piece lubric plastic bearing confined in said pocket and having vent holes communicating between the pump chamber and the shaft housing, a shaft extending in clearance relation through said shaft housing to define a vent passage communicating between the vent holes in the pump and shaft housings and having a lower end journaled in said bearing and carrying an impeller for rotation in said pump housing and float operated control means for regulating the liquid level of the sump.

2. Cryogenic circulation apparatus comprising a main housing having a dewar vessel disposed therein and providing a thermally isolated sump for storing a reservoir of cryogenic liquid, said main housing also defining a chamber alongside the dewar vessel and exposed to normal ambient conditions, said main housing having a cryogenic liquid inlet opening into the sump, a cryogenic liquid discharge line emerging upwardly through the dewar and main housing, pumping mechanism carried by said main housing and including a shaft housing fixed to said main housing and extending vertically to terminate at a lower end submerged in the cryogenic liquid, said shaft housing having vent openings above the level of the liquid in the sump, a pump housing fixed on the lower end of said shaft housing and defining a pump chamber, said pump housing having an axial top pocket opening upwardly into the shaft housing, an axial bottom inlet opening into the sump and a peripheral discharge outlet communicating with said discharge line, a one piece lubric plastic bearing confined in said pocket and having vent holes communicating between the pump chamber and the shaft housing, a shaft extending through said shaft housing, said main housing including support structure surmounting the dewar vessel, and a carrier mounted in elevated relation on said support structure and supporting an external bearing, said shaft having a lower end journaled in said one piece bearing and carrying an impeller for rotation in said pump housing and said shaft having an upper end equipped with a pulley and supportedly journaled in said external bearing, said support structure having means cooperable with said carrier for effecting elevational adjustment of the external hearing for varying the axial position of the shaft, and float operated control means for regulating the liquid level of the sump.

References Cited UNITED STATES PATENTS 2,760,437 8/1956 Di Stefano 103-113 761,730 6/1904 Tucker l03103 2,829,598 4/1958 Zimmermann et al. 103-26 2,888,879 6/1959 Gaarder l03153 3,010,402 11/1961 King 10397 3,220,202 11/ 1965 Gottzmann 62-55 2,932,310 4/1960 Koblish 6255 3,274,938 9/ 1966 McCracken 103-11 FOREIGN PATENTS 808,796 12/ 1951 Germany.

DONLEY J. STOCKING, Primary Examiner. W. L. FREEK, Assistant Examiner. 

